What’s probably most disappointing to those who predicted the Celtics’ demise is that they truly believed the team would disappear quietly into the sunset, a bunch of jumbled pieces dissolving into insignificance because their most prominent player was gone.

Instead, the Celtics are very much alive, much to the chagrin of their detractors and their Eastern Conference rivals who believed Boston was finally finished in its current state. The Celtics have spent the past five weeks shaking off the disappointment and bewilderment left by season-ending injuries to Rajon Rondo and Jared Sullinger and actually pushing forward with a refurbished product — and with success, going 13-4.

Although the Miracles churned out 14 Top 20 hits with Smokey Robinson as lead singer, they still enjoyed success as a retooled group with Billy Griffin. They weren’t the same, perhaps not as appealing on the surface, but they worked together to produce a more-than-acceptable sound.

The Celtics have worked feverishly to produce a more-than-acceptable product, one that could take them past the first round of the playoffs and into a head-to-head matchup with the Pacers, Knicks, or Heat, three teams considered clearly superior to the Celtics once Rondo went down.

And they still may be. But what the Celtics have proven is that their depth — something president of basketball operations Danny Ainge wanted desperately to provide around his aging core — is beginning to pay dividends.

Jeff Green is playing as if he wants to be a primary option instead of humbly conceding the scoring responsibility to Paul Pierce or Kevin Garnett.

The presence of Avery Bradley and the effect of his defensive prowess on his teammates has been stunning.

After languishing near the middle of the pack defensively (17th) before the first of January, the Celtics have risen to ninth in points allowed; six of their 17 opponents during Rondo’s absence have scored 89 points or fewer. On offense, their balance and versatility have been effective weapons.

While Garnett has remained steady, Pierce has been erratic at times, battling injuries. But that has allowed Green to flourish, as well as Bradley, Courtney Lee, and Jason Terry on occasion. And while the Celtics played with passion during Rondo’s tenure, more attention is now being paid to detail, with the players acknowledging a smaller margin for error.

With Rondo in the lineup, the Celtics lost a whopping 15 games by double digits; they have lost just once by 10 points in the past five weeks. Plainly stated, the Celtics are a difficult out and are more passionate later in games because they understand Rondo can’t rescue them with a late hustle rebound or improbable pass.

The reinvented Celtics have regained their confidence and stride after being knocked off the path by a midseason tornado.

“People who wrote us off didn’t know really who we are,” Garnett said. “I think half the journalists out there don’t even watch basketball. They just talk. I really don’t know what it is, we really don’t care. Right now, we’re focused on what we’re doing in here.”

The Celtics have flourished under the radar. Their Jan. 27 victory over the Miami Heat was attributed to emotion and adrenaline after the news of Rondo’s knee injury surfaced that morning.

But as the post-Rondo era progressed, the Celtics gained more comfort with their current state. It began when coach Doc Rivers declared that the Celtics weren’t prepared to hold a garage sale of veterans after the injuries, and it seems that players such as Green, Lee, and Terry responded to the added responsibility, seemingly relieved that they had more of a stake in the team’s success.

There were placed inside Rivers’s circle of trust because the coach had no other choice. And all three have relished the renewed confidence after struggling in the first three months. Because of Bradley’s presence and Green’s resurgence, Lee is a shooting guard who doesn’t necessarily need to shoot. Terry thrives in the new ball-movement offense because he receives passes in more favorable spots, not just coming off screens.

This rejuvenated product is intriguing because its potential remains unknown. Without Rondo dominating the ball and orchestrating the offense, the Celtics have become the league’s biggest enigma, an unknown entity that is a potential dark horse in the Eastern Conference.

The Celtics aren’t the same without Rondo, and as soon as the players realized that, going with a revamped style and renewed passion, they were better prepared to salvage this season. Their recent surge has increased expectations. They plan to play as long they’re allowed to, focusing on those who are present and spinning hits with their new band members.

So far, the sound is a catchy melody.

“Like I was always said, from the outside, people don’t matter in our locker room and what we’re trying to do,” Lee said. “Even if we make the playoffs, they’re going to have something else to say.

“They doubted that we were going to make it because Rondo went down and Sully went down, then when we get there, we’re not going to make it past the first round, so it’s going to be fuel to the fire and motivation. That’s all.”